How Air Brakes Work on a Truck
// July 7th, 2010 // No Comments » // Uncategorized
Because a runaway truck could result in a much worse outcome than a car with a brake failure, tractor-trailers are designed to use air brakes. While traditional vehicles rely on hydraulic fluid for the proper functioning of their braking system, air brakes rely on the air that surrounds us all. The theory is that there is less potential for failure of the system if you don’t have any fluid to leak. As an additional safety feature, air brakes will lock up and stop the truck immediately if they fail as opposed to hydraulic brakes that don’t work at all during a failure.
Truck Air Brakes
The air brakes on large trucks operate on the triple-valve principle where air pressure must build up inside the pipes to release the brakes. Most systems feature a graduated release system where a partial build up will result in a proportionate release of the brakes. Those odd squeaking and hissing noises that you hear coming from a parked truck are a result of the operation of the air brakes. The squeaking occurs as air is released from the brakes, and the hissing comes from the bypass safety valves maintaining the air pressure at the correct pressure. Air brakes are also the reason why trucks must usually sit for a few minutes when first started so that the brake pressure can build.
The Basic Principle
George Westinghouse invented air brakes in 1869 for the railroad industry, and their basic operation remains the same to this day. Westinghouse’s triple-valve air brake system consists of three basic functions. The first step is charging. The system must be brought up to pressure before the brakes can be released. The second step is when the brakes are applied. During application, air pressure drops and air flows back through the valve into the reservoir tanks. During the final release step, the pressure is again increased. Logically, this sounds backwards to most people who normally use hydraulic brakes. With a normal vehicle, you stop as apply more pressure. With air brakes, you stop as you reduce the pressure.
Brake Failure
While we often hear about problems with air brake systems, a total system failure is extremely rare. Most trucks are equipped with emergency air brakes in case the primary system fails, and some trucks also have an exhaust brake system that is powered by the engine instead of the air system. With all backup systems taken into consideration, it’s still possible for an accident to occur because of faulty brakes if proper maintenance is not performed.
Legal Resource: Truck Accident Attorney Jeff Seely
